If anyone remembers a TNG episode from Season 3 called "Who Watched the Watchers", a proto-Vulcan culture was being studied by a Federation science team in anonymity when the holo generators hiding their location fail and they're discovered. This proto-Vulcan culture was portrayed as being Vulcan-like with logical attributes, the Vulcans of TOS or TNG, that is. Vulcans were barbaric and warlike in their past, so one would expect a proto-Vulcan culture to be similar, but this was not the case, and is very much a bad mistake similar to the type made in Nemesis where something was overlooked from Star Trek history, and Gene was still alive then. In that case, since this ptot-Vulcan culture (the Mintakans) arent actually Vulcans, they could get away with it.
On another note, I've just watched all of Eneterprise for the first time on DVD (never watched it all when it was shown on TV).
Seasons 1 and 2 seemed to have a lot of discrepencies with Trek history, I thought the Temporal Cold War was an interesting concept but could have been dealt with far better and the time travel story arcs have been overdone in Trek. Season 3, I thought was the worst. Far too preoccupied with the whole Xindi story arc (a race which apparently doesnt exist in TOS or TNG) and portrayed Archer as a captain all too willing to sacrifice morals and make bad decisions. The episodes themselves were enjoyable to watch and creative, and being creative and writing good sci-fi is something Trek has always been about. But... this material would have been better presented either in a Trek series set in post-TNG, or in another series all together.
Season 4... in stark contrast, was absolutely excellent!! Its quite clear that the new writers for Season 4 went above and beyond the call of duty in trying to account for or explain all the screwups of the previous seasons. They managed to restore the Vulcans to their nature as presented in TOS (Vulcans seemed to be very un-Vulcan-like in the first 3 seasons), got rid of the Temporal Cold War in the first episode (as though it never hapenned in the true Trek timeline) and even managed to explain why the Klingons had no ridges in TOS!! The Mirror episodes were brilliant! I liked how the writers (Garfield and Judith Reeves-Stevens) also drew upon content from original fiction as well, which is particularly prevalent in the episode "The Forge" and the mini-story arc about Surak. (Vulcan's Forge was a hard cover novel from Pocket Books published about 10 years ago).
My only criticism of Season 4, is the last episode, which seemed to be an anti-climax. The penultimate episode seems to be where the series really ended. Marina Sirtis and William Frakes just seem to be showing their age a bit too much (Sirtis appears to have given up trying to put on an American accent) to have set this episode during TNG somewhere. Overall though, if the rest of the series had been like Season 4, I think Enterprise would still be in production now. A case of too little too late.